The document discusses the development of scientific theories and experiments regarding atoms, light, and quantum mechanics. It describes early experiments and observations that led to discoveries such as the planetary model of the atom, the particle nature of light, and wave-particle duality. Later, quantum mechanics was developed to explain the intrinsic unpredictability of atomic behaviors and experiments such as the double slit experiment.

1. Big Questions in Science

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3.  Color and spectra
 Atoms
 Schrödinger’s cat
 Radioactivity
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4.  Light is a wave made of
different wavelengths
 Blue light has short
wavelength. Scattered all around atmosphere.
Ni (78%)
O (21 %)
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6.  Cathode ray tube
1. Three electron guns
2. Electron beams
3. Focusing coils
4. Deflection coils
5. Anode connection
6. Separating beams
7. Phosphor layer
8. Close-up of screen
http://en.wikipedia.org/wiki/File:CRT_color_enhanced.png
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7. • (Semi-) vacuum tube
• Metal electrodes, high voltage in between
• Postitively charged atoms attracted to cathode (neg.)
• Kicked off electrons attracted to anode (positive charge)
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8.  Faraday: electrical current bent by a magnet.
 Thomson: electrical current consists of
particles much smaller than atoms.
 Mass 1600 smaller than hydrogen.
 Röntgen: new type of ‘cathode’ radiation.
Becquerel: uranium emits Röntgen radiation.
Marie Curie researched other substances.
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10.  Ernest Rutherford: radiation consists of:
 Beta-rays. Could be bent, electrons.
 Alpha-rays. Could be bent, much
heavier, positive charge. Helium ions.
 Gamma-rays. Röntgen radiation. UV
 Suggested internal structure of atoms.
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11.  Rutherford: researched thorium, found
emanation and radioactivity. Bombarded
platinum foil with alpha particles, reflected in
all directions.
 Conclusion: mass
concentrated in the
nucleus.
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12.  Rutherford: second, “planetary” model
(inspired by Lord Kelvin).
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14. Different elements have different ‘absorption spectra’, specific wavelengths that they
absorb (or emit).
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15. Planck’s law
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16.  Assumption Planck needed to make: light
carries energy in discrete amounts.
 Each ‘energy packet’ has energy h
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17.  Fascinated by planetary model.
 Putting things together: quantum hypothesis
applied to atom.
 Atomic numbers explain
properties of atoms.
 Sommerfeld refined version.
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19.  Radiatioactive decay is random.
 Same true for photon emission by atom:
unpredictable.
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20. PET scan X-rays
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21.  As long as radiation is not measured, the
atom is in two states (decay/non-decay). This
is called a superposition.
 Property is only determined once a
measurement is made.
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22.  The single-slit experiment
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23. http://www.universetoday.com/83380/double-slit-experiment/
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24. http://www.hitachi.com/rd/research/em/doubleslit.html
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25. Waves that go through the slits interfere with each
other.
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http://russherman.com/Talks/FirstThreeMinutes_CollegeDay.pdf

26. http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/
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27.  Electrons and photons behave as waves while
in transit: interference.
 Detected as particles on the screen.
 Interference pattern disappears if
observation.
 No way to predict where single photon ends
up: intrinsic unpredictability. Only
probabilities.
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28.  de Broglie: if photons are both waves and
particles, particles behave as waves.
 Planck relation: . Matter: .
 Frequency proportional to speed (squared).
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29.  Waves of high frequency (short wavelength)
are sharply localized, waves of low frequency
(long wavelength) are spread out.
Small Large
Large Small
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30. Electron microscope Quantum computing
http://www.science.uva.nl/onderwijs/thesis/apart/phys/thesis.php?start=181&level=bachelor
Resolution ~ wavelength
0.1 to 0.5 nm
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34.  Compare Bohr’s model of the atom with the
Solar System.
 1) Similarities. 2) Where analogy breaks down.
 What is the role of the hydrogen atom in the
development of modern quantum
mechanics?
 Hint: consider Kuhn’s notion of ‘exemplar’.
 Think of similar examples in Newtonian physics
and in the theory of relativity.
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